Propelling mechanism



June 2l, 1960 F. H. PHILBRICK PROPELLING MEcHANIsM June 21, 1966 F. H. PHILBRICK PROFELLING MECHANISM 6 Sheets-Sheet 2 Filed April 50, 1954 F. H. PHlLBRlcK 2,941,481

PROPELLING MECHANISM .Fume 2i, 1960 Filed April 30, 1954 6 Sheets-$heet 3 June 21, 1960 F. I-I. PI-IILBRICK 2,941,481

PROPELLING MECHANIsI/I Filed April 30, 1954 6 Sheets-Sheet 5 I I I I I I I I I Iv I I I I I I I I I I I I I I I I I June 21, 1960 F. H. PHILBRICK 2,941,481

PROPELLING MECHANISM Filed April 30, 1954 6 Sheets-Sheet 6 Fran H. Philbrllck United States Patent PROPELLING' MECHANISM Frank H. Philbrick, Evanston, Ill. (122 S. Michigan Ave., Chicago, Ill.)

Filed Apr. 30, 1954, Ser. No. 426,836 3 Claims. (Cl. 10S-31) The present invention relates to propelling mechanism for vehicles and has particular reference to track-supported equipment such as trackworking or ballast-removal apparatus wherein advance of the equipment is resisted by forces which are in excess of the tractional forces capable of being exerted by the vehicle Wheels during normal propulsion of the vehicle along the roadbed.

For example, in a machine for digging and elevating ballast from the sides of the track and cleaning and returning it to the roadbed, the machine is tractionally driven by the vehicle wheels to advance the digging and elevating mechanism to progressively dig or remove the ballast, and, at times, it is found that the traction between the truck-wheels and the railway rails is inadequate for propulsion when the digging or earth working mechanism is in operation.

One object of the invention is to provide propelling mechanism which reacts to a tread which is periodically applied to the roadbed with a degree of force which is substantially in direct proportion to the forces tending to resist advance of the vehicle along the roadbed. Another and important object of the invention is'to provide a propelling mechanism of the character briey outlined above wherein the tread which is periodically applied to the roadbed for traction purposes is positively forced against the roadbed by a novel and true toggle action involving toggle devices having toggle links attached at their free ends to the vehicle frame and traction tread respectively, together with means for periodically effectively applying force to the links at or near the toggle elbow in a direction tending to straighten out the toggle device so that the latter, in so moving toward its straightened position, exerts opposite and equal forces against the traction tread and vehicle frame whereby the superior gravitational force ofthe vehicle frame drives the traction tread, so to speak, rmly into tractional engagement with the roadbed. In carrying out this last mentioned object, due to the superior gravitational force of the vehicle frame, and due to the fact that the maximum toggle spread is greater than the effective distance between the frame and tread, the toggle devices attain a locked condition wherein further spreading action is impossible, and, when such a condition obtains, the toggle devices then become non-yielding reaction members against which propulsion force may be applied to drive the vehicle forwardly. Furthermore, due to the fact that the toggle devices are attached to the vehicle frame and traction tread, forward propulsion of the vehicle frame will tilt the toggle devices bodily, as a unit, forwardly on the traction tread, thus slightly increasing the spreading action of the toggle devices and very materially increasing the toggle action so that a powerful and progressively increasing thrust is applied to the vehicle frame during any given cycle of operation to its final propulsive movement during such cycle.

Other objects of the invention are to provide propelling mechanism of this type: which is simple in construction and ecient in operation; which is adjustable for propelling the truck at variable speeds to conform to the capacity ice 2 of the apparatus or the resistance of the ballast; which is adjustable for operation along railway tracks including rails of different heights; and which includes other improvements which will appear from the detailed descrip tion.

The invention consists in the several novel features which are hereinafter described and more particularly deiined by the claims at the conclusion hereof.

In the drawings: y

Fig. 1 is a longitudinal section taken on line 1- 1 f Fig. 3, parts being broken away, of a truck or vehicle equipped with propelling mechanism embodying the invention, said mechanism being shown in full lines at the commencement of an advancing stroke, and in dotted lines at the end of an advancing stroke;

Fig. 2 is a longitudinal section taken on line 2 2 of Fig. 3 showing the propelling mechanism in full lines at the end of an advancing stroke of the frame structure and in dotted lines at the end of an advancing stroke of the traction tread relatively to said structure; I

Fig. 3 is a transverse section taken on line 3-3 of Fig. l, parts being broken away;

Fig. 4 is a section taken on line 4 4 of Fig. 1;

Fig. 5 is a detail view of the clutch for selectively cotrolling the gearing for operating the toggles;

Fig. 6 is a detail of the adjustable fulcruin for the crank-operated lever;

Fig. 7 is a longitudinal section taken on line 7-7 of Fi 3;

tclig. 8 is a transverse section illustrating a modification which includes alternately operated mechanisms for propelling the truck in a continuous succession of advancing strokes; and

Fig. 9 is a schematic view representing the geometrical relationship involved in connection with certain toggle devices and linkage mechanisms employed in connection with the present invention.

The invention is exemplified in a vehicle or truck on which digging apparatus of any type is mounted for operation along a railway track, for example, apparatus for digging ballast along the sides of the track and conveying it to cleaning apparatus on the truck, and returning the cleaned ballast to the roadway, as set forth in United States Patent No. 2,272,429. The truck or vehicle is equipped with wheels adapted to travel on the lrails of the railway track and mechanism for driving said wheels when the apparatus is idle and being transported to or from places of use along the track, and the traction between said wheels and the rails is suiiicient for speedy travel.

The truck is equipped with selectively operable mechanism for propelling it on its wheels and along the railway track at the slow rate of travelfor example, 1,000 to 1,500 ft. per hour, as required by the capacity of the digging or other apparatus, `and for which traction between the truck-wheels and the -rails is inadequate. Said mechanism is adapted to react to a traction. tread which is periodically applied to the roadbed for propulsive purposes and thereafter released from the roadbed and advanced to a new position for the next successive application to the roadbed. y

The invention is exemplified with a truck or vehicle embodying a rigid frame-structure for supporting any desired digging, conveying and cleaning or other earth Working apparatus. This frame-structure is mounted on a pair of rear wheels 20 which are adapted to travel on the rails 21 of a standard railway track and are connected by an axle 22, and a pair of front wheels 23 which are connected by an axle 24. The frame structure comprises longitudinal beams 25 with dependent bearings 26v for axles 22 and 24; transverse beams 27 and 28, longitudinal beams 29 and a platform 30. Beams 25, 27, 28 and 29 and platform 30 are all rigidly secured together and provide a rigid frame-structure or support for the digging and otherapparatus and a power plant,

This power plant on the truck usually includes a motor, a Clutch, and variable speed transmission, diagrammatical- 1y`shown, generally designated 33 and mounted on platform 30, and an output shaft 32, which is provided with a belt pulley 34 which drives belt 35 and a pulley 36 which is driven by belts 35 and secured on a countershaft 37 which is journalled in bearings 38 on beams 25. A clutch 41 on shaft 37 is adapted to selectively vdrive a pulley on said shaft, belts 42 and a pulley 43 on axle 22 for'rdriving said axle and wheels 20. Clutch 41 controls the operation of wheels 20 by power from shaft 32 and may be controlled by the operator through any suitable means on the machine. This driving mechanism is adapted'to speedily propel the truck or vehicle to and from the place along the railway track where Work is to be performed.

, The power-'driven mechanism is designed for coopera- `tion with a traction or reaction tread 44 which is supported on the truck and intermittently functions as a fixed back stop or abutment on the roadbed against which said mechanism reacts, when the ballast is being progressively displaced from the shoulders of the roadbed by diggingmechanism on the truck. At such times, the in- :creased propulsive power necessary for propelling the truck with apparatus mounted thereon, is provided by the propelling mechanism which reacts against the traction tread.

' l The traction tread 44 'includes a shoe 45 of channel cross-section which extends longitudinally and centrally of the rails of the track, and a rubber or elastic sole or liner 46 for frictional and pressure engagement with the ballast and the ties of the roadbed. The tread 44 is operatively suspended from the frame-structure by a pair of toggles, each of which includes a lower link having its lower end pivoted to the shoe and an upper link having its upper end pivoted to the frame-structure and its lower end pivoted to the upper end of the lower link. The front toggle includes a lower link 50 pivotally connected by a pin 51 to the shoe 45, an upper link 52 which is pivotally connected by a pin 53 to a longitudinal channel bar 54 which is rigid with and forms a part of the frame-structure of the truck and a pin 55 pivotally connecting the upper end of link 50 and the lower end of link 52. The rear toggle includes a lower link 57 which has its lower end pivotally connected by a pin 58 to shoe 45, and an upper link 59 which is pivotally connected by a pin 60 to bar ,54 and has its lower end pivotally connected by a pin 61 to the upper end of link 57. The lower toggle links 50 and 57 are interconnected by a bar and lever assembly including a bar 64 and a lever 66 pivotally connected by a pin 68 at adjacent ends. The bar 64 has its rear end pivoted as at 65 to a medial region of the link 57, while the lever 66 is itself medially pivoted as at 67 to a medial region on the link 50. The lever 66 projects forwardly and downwardly beyond the forward ends of the front toggle and carries at its forward lower end a pin 68 vby means of which it may be operatively connected to certain power-actuated mechanism7 the nature and function of which will be made clear presently.

The above described toggle mechanism including the front toggle links 50, 52 and the rear toggle links 57, 59, together with the connecting linkage structure 64, 66, when considered as a whole, operates in its entirety as a unidirectionally movable spreader mechanism between the vehicle frame and traction tread for spreading these members apart during each cycle of operation thereof while the vehicle frame moves forwardly. The application of force to the pin 68' tending to force the lower forward end of the lever 66 rearwardly and downwardly and thus rotate the lever in a clockwise direction as seen in Fig. l, will exert a component of rearward thrust on the elbow portion of the front toggle tending to straighten out the same. Due to the relatively great gravitational mass of the frame and its load, the front end of the traction tread 44 is forced downwardly into contact with the roadbed :until such time as the front toggle reaches an impasse wherein it Yisunable to exert sufficient lifting force on the frame to move the same. At this time the front toggle becomes locked and the front end of the tread 44 is in such hrm contact with the roadbed that slippage is impossible. Since the combined effective length of the links 50 and 52 is greater than the effective height ofy theV frame above the roadbed, any increased application of force on the pin 68' would either disrupt the roadbed, ie. shift the ties, or lift the frame. According to the present invention, rupture of the roadbed or lifting' of the'frame is made impossible during normal operation of the digging apparatus due to the Vfact that the force which is applied toward movement of the pin 68' is a spreading force'which is applied between the pin and the frame and which has its resultant vectorial direction of force applied to the frame so as to propel the frame forwardly along the roadbed. This force may be derived by the spreading action of a piston and cylinder interposed between the frame and pin v63', by a hydraulic jack arrangement, by a lever 'of the first, second or third class applied between the pin and a fixed point on the' frame, or by a system of linkages operable under the control of a power driven crank arm such as has been illustrated herein for exemplarypurposes and which will be described in detail subsequently.

Due lto the fact that the relatively great gravitational weight of the frame and its load is superior to any retarding force which normally will resist forward travel of the vehicle frame along the roadbed, and due to the fact 'that the frame and the pin 63 constitute reaction members, each for the other, it is the frame which will yield .and not the front toggle assembly 5t), 52. This front toggleassembly as a whole thus becomes an unyielding reaction member between the frame and roadbed and it operates as a springboard from which forward motion of the vehicle frame may take ott" when proper force is applied between the toggle assembly and frame having the necessary vectorial direction to force the frame forwardly along the roadbed.

It is to be noted at this point that as the vehicle frame moves forwardly vunder the impetus of reaction between the pin 68' and frame as will be described presently, the already locked toggle assembly 50, 52 will rigidly rock or tilt forwardly about the axis of the pin 51 and, in so rocking, the toggle spread will increase slightly so that the angles involved will change, with the angle at the toggle elbow approaching The geometrical relationships involved are shown in Pig. 9. In this View the pin 68' is operatively connected to the frame bar 29 by a link 69 and a lever 91, the latter being capable of being oscillated by means of a crank arm 72 operable under the control of the motor 33. The lever 98 iS pivoted at 96 to the frame bar 29. The parts schematically shown in Fig. 9 and mentioned above will have their counterparts in the operative mechanism for applying torque to the pin 68 and which will be described in detail presently. It will be seen that upon application of force to the pin 68 by the lever 9S in the direction indicatedby the arrow in Fig.. 9, the lever 66 will move in 'a clockwise direction, thus forcing the pin 67 to the left and pulling the bar 64 and pin 65 to the right. This actionon the pins-61 and 67 will tend to straighten out both the front and rear toggles equally, thus lowering the tread 44 uniformly to the roadbed and forcing the former firmly into frictional engagement with the latter until the toggles can no longer move toward their fully straightened positions. The toggles then become locked and only such force on the pin 68' as can overcome-the disinclination of the frame bar 29 to rise can move the toggles. t9 their ultimate 180 positions. This amount of force however is unattainable because the additional force applied to the pin 68 by the lever 91 and link 69 will exert a forward thrust on the pin 96 tending to propel the vehicle forwardly. The ability of the vehicle to yield to forward motion is under all normal conditions less than the superior force of gravity acting on the frame bar 29.

-It is to be further noted that for eiiicient operation of the toggle mechanisms and their connecting linkages, the pin 67 is disposed on the link 50 above the mid point of the link while the pin 65 is similarly disposed on the link 57 above the mid point of this latter link. Preferably, the distance between the pin 67 and the mid point of the link 50 is less than the distance between the pin 65 and the mid point of the link 57.

The power driven mechanism for actuating the toggles to apply the traction tread to the road bed and advancing the tread relatively to the truck frame, comprises: a clutch 83 on countershaft 37 which is driven from the motor by belts 35 and pulley 36; a sprocket wheel 81 selectively operable by clutch 83; a chain 82 driven by sprocket wheel 81; a sprocket wheel 80 on a cro-ss shaft 77 and driven by chain S2; a sprocket wheel 76 rotatable with sprocket wheel 80; a sprocket chain 75 driven by sprocket wheel 76; a shaft 70 journalled in a`bearing 71 fixed to beam 54; a sprocket wheel 74 fixed to shaft 70 and driven by sprocket chain 75; a crank pin 72 on a disk 73 which is fixed to a shaft 70 and functions as a crank; a lever S6 fulcrumed on a pin 85 supported in a hanger 8'7 which is adjustably iixed to one of the beams 29 of the frame structure and provided with a slot SS in which crank pin 72?. is slidable; a connecting bar 89 which is pivotally connected by a pin 90 to the distal end o'f a lever S6, a lever 91 which is pivotallymounted ona shaft 96 which is supported in bearings 94 on the beams 29 and includes an upwardly extending arm 93 to which the front end of bar 89 is pivotally connected by a pin 92, and a depending arm 98; and link 69 which has its front end pivotally connected by a pin 97 to the lower end of arm 98 of lever 91 and its other end pivotally connected by pin 68' to the lower end of lever 66.

Shaft 70, during each forward cycle of substantially a one-half revolution, will operate crank-pin 72 to oscillate lever 86 and operate bar S9 forwardly relatively to the frame-structure. Bar S9 will exert forward stresses at pin 92 on the upper end of the arm 93 of lever 91 to rock said lever on the axis of shaft 96 and exert rearward thrust on the lever 69 and pin 63.

Such rearward thrust on the pin 65 will effect toggle movements as previously described in connection with the schematic disclosure of Fig. 9 with the spreading reaction force existing between the pin 68 and pin 96 applying a forward vectorial component of thrust to the latter' pin and serving to advance the vehicle frame forwardly along the roadbed.

During the rearward motion of crank-pin '72, lever 91 will swing on the axis of shaft 96, relatively to the framestructure, and exert a forward and upward pull on link 69, which will move the lever 69, bar 64, the lower toggle links and the traction tread, forwardly and upwardly so the tread will clear lor slide over the roadbed at the end of the rearward cycle of pin 72. The traction tread and toggles will be positioned for the commencement o-f an advancing stroke of the truck, as shown by dotted lines in Fig. 2. It is to be noted that such rearward motion of the crank pin 72 takes place while the pin is in the lower regions of the slot 88 so that a relatively rapid return motion of the lever 86 will take place, thus insuring quick withdrawal of the tread 44 from engagement with the roadbed.

The height of the railway rails varies on different railways. For adapting the auxiliary propelling mechanism for use with rails of different heights, the pivot pins 53 andl 60, on which the upper toggle links 52 and 59 are suspended, are verticallyadjustable on the beam 54l of the frame-structure. Ribs 101 on beam 54 are engaged by the hubs of the upper links of the toggles for trans mitting horizontal thrust to said beam. When the truck operates on tracks with rails of different heights, the vertical distance varies between the roadbed and the frame-structure on which the toggles are suspended. Such variation would cause angular relative variation of the links of the toggles when the head 44 is lowered to engage the roadbed. It is advantageous to maintain predetermined relative angular relation of the links of the toggles for the desired coelicient of traction between the roadbed and the tread and for that purpose the toggles, lever 66 and bar 64 are unitarily adjusted to operate within the same vertical range relatively to the roadbed. The pins 53 and 60 are adjusted vertically on the frame-structure so that when the tread 44 is on the roadbed between rails of different heights, the pre; determined relative positions of the toggles and their links, lever 66 and bar 64 will not be substantially changed and the effective pressure of the tread on the roadbed will be substantially the same.

In practice, it is desirable to vary the length of the advance stroke of the trunk during each forward cycle of the lever 86 for varying the speed of advance of the digging apparatus on the truck according to the capacity of said apparatus to dig or handle ballast -or other material of different densities. For this purpose, lever S6 is adjustable to vary its stroke and the length of the forward stroke of bar 89 during each cycle of one-half revolution of shaft 70 and crank-pin '72. The ful'crumpin S5 for lever 86 is supported on bracket S7 which is vertically adjustable on one of the beams 29 by means of bolts 104 and Vertical series of holes 103 in said beams. When the pin is adjusted upward, the distance between crank-pin 72 and fulcrum-pin 05 of lever S6 is shortened and the stroke of pin 90 on distal end of lever 36 is increased. This increase of stroke increases the forward stroke of bar 89, lever 91 and shaft 96 and the advance of the truck correspondingly. When the pin 85 is adjusted downwardly the distance between crank-pin 72 and fulcrum-pin S5 will be increased and movement of the distal end of lever 86 will be decreased to correspondingly decrease the forward stroke of the bar 89 and arm 93 of lever 91 and correspondingly decrease the length cf the advance stroke of the truck during each forward cycle of crank-pin 72.

When the machine is propelled from the truck wheels 20 for transporting it to and from places where work is to be done, the traction tread is lifted to clear the roadbed. A cable connected at 106 to bar 64 and guided by a sheave '107 on the frame structure, is connected to a stem on a piston 109 in an air cylinder 108 mounted on platform 30. A valve 111 `controls the ow of compressed air to and from the cylinder for operating the piston 109 to pull cable 105 for raising the bar 64 and the lower links of the toggles so that the traction treadV will travel above the roadbed and clear the track rails. When the valve 111 is set to admit compressed ai-r to cylinder 108, piston 109 will pull cable 105 to hold bar 64 and the toggles raised to support the traction tread above the roadbe When valve 111 is set to exhaust air from cylinder 10S, the traction tread will be lowered by gravity into operative range with the roadbed withk slack in the cable to permit the aforesaid actuation of the toggles.;

In the form of the invention shown in Figs. l to 7, there is a single traction tread and intermittent strokes are applied to the toggles to advance the truck while the-- on the roadbed with alternatestrokes to release and advance the traction tread. This traction tread -is anchored intermittent advance is advantageous when digging machanism is subjected to extreme resistance by the ballast or other material. In some instances where the Work per-- mits, it is advantageous to continuously advance-the ma-' chine by consecutive strokes. A modification for v7 continuous advance is illustrated in Fig. 8 and comprises a pair of propelling mechanisms which are substantially alike in construction and are operated alternatelyand consecutively to continuously advance the truck.

Each of said propelling mechanisms includes, a traction tread 44, a toggle system including front and rear toggles, a lever 66, a bar 64, a link 69, a lever 91, a bar 89 and a lever 86 of the construction shown in Figs. l to 7, and operating individually as before described, but they are co-related to alternately produce advance strokes of the truck in continuous succession. Beams 54 for supporting the toggles of the propelling mechanisms are included in the frame-structure. This succession is accomplished by a shaft 112 which like the shaft 70 in Figs. 1 to 7 is driven by like gearing from the clutch 83. Shaft 112 extends transversely between and is journalled in bearing 113 on beams 25 and a bearing 114 on one of the beams 4. Shaft 112 is provided with a pair of cranks 115 which are disposed 180 apart. Each crank extends through a slot S8 in a lever 86. A sprocket chain drive 116 is used to drive shaft 37 in lieu of the belt drive shown in Figs. 1 to 7.

In operation of the modification shown in Fig. 8, each of the levers 91 will actuate one set of toggles to anchor one traction tread on the roadbed and be operated to advance the frame-structure, and alternately lift and advance the tread relatively to the frame-structure and the advance of the frame-structure by said levers will be in continuous succession.

Each crank-pin 72 is arranged to traverse the lower portion of slot 88 nearer to the fulcrum-pin 85 during the backward movement of bar 89 or `the advance of the tread 44 relatively to the roadbed and to traverse the outer end of said slot during the forward movement of lever 86 and bar 89, so that the tread will be moved more rapidly during its idle stroke than the bar 89 is moved during its operation to advance the truck. Y

The invention is not to be understood as restrictedvto the details set forth, since these may be modified Within the scope of ythe appended claims without departing from the spirit and scope of the invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: 4

1. Driving mechanism for the forward propulsion of a vehicle provided with wheels and having a frame for supporting roadbed material-removing apparatus, said mechanism comprising front and rear toggles pivotally suspended from the frame, each toggle including yan upper and a lower link, said links being pivotally connected together at adjacent ends to provide an elbow joint, the upper end of each upper link being pivoted to the frame at longitudinally spaced points therealong respectively, and 4the lower end of each lower link being pivoted to the tread at longitudiinaililiy spaced points therealong respectively, the combined length of the upper and lower links of each toggle being greater than the effective distance between their respective po-ints of pivotal connection to the frame and tread when the latter is in firm contact with the roadbed, a lever pivoted medially of its ends to a medial region of the lower front toggle link above the mid-point of the latter, having its rear end disposed rearwardly of the point of pivotal connection for the lever on the lower front toggle link and above said point, a bar having its rear end pivoted to a medial region of said lower rear toggle link above the mid-point of the latter and having its front end pivoted to the rear end of the lever, the distance .between the midpoint of the lower front toggle link and its point of pivotal connection with the lever being less than the distance between the midpoint of the lower rear toggle link and its point of pivotal connection with the rear end of said bar, extensible and contractible instrumentalities extending between the front end of said lever and the frame and operable upon expansion thereof to apply force to said front end of the lever in a direction having a `rearward vectorial component of motion and to simultaneously apply force to said frameY in a direction having a forward component of motion whereby, a component of rearward force will be applied through the lever to its point of pivotal connection with the lower front toggle link tending to straighten out the front toggle and rigidify the latter between the frame and tread as the latter engages the roadbed, and whereby ar component of forward pull will be applied by the lever to the bar and, through the bar, to its point 'of pivotal connection with -the lower rear toggle link tending to straighten out the rear toggle and Irigidity the latter between the frame and tread as the latter engages the roadbed, and whereby the frame will be moved forwardly as the lower front and rear toggle links swing pivotally on the tread, and means for extending and contracting said extensible andl contractible insbrumentalities. Y

2. Driving mechanism for the forward propulsion of a truck or vehicle as set forth in claim 1 wherein said extensible and contractible instrumentalities comprise a link connected at one end to said front end of the lever, and a second lever pivoted medially of its end to a tixedpoint on the frame, the other end of said latter link being pivotally connected to the lower end of the second lever, a crank mounted for rotation on the frame and having an eccentric crank arm, means operatively connecting the upper end of the second lever and crank arm in driving relationship whereby rotation of the crank will eifect oscillation of the second lever, a motor mounted on said frame, and means operatively connecting the motor and crank in driving relationship.

3. Driving mechanism for the forward propulsion of a wheeled vehicle on a roadbed, said vehicle having a frame, said driving mechanism comprising an anti-friction traction tread engageable with the roadbed and movable vertically between an elevated linoperative retracted position out of engagement with the roadbed and a lowered operative advanced position in frictional engagement With the roadbed, front and rear extensible and contractible toggles each including an upper link pivoted to the frame at longitudinally spaced points therealong and a lower link pivoted to the tread at longitudinally spaced points therealong, said upper and lower links being pivoted to each other to provide a toggle elbow joint, a lever pivoted medially of its ends to the medial region of one link of one of said toggles and projecting forwardly and rearwardly on opposite sides of said one toggle, a bar having one end connected to the rear end of said lever and having its other end connected to one of the links of the other toggle medially of said latter one link, the combined length of the links of each toggle being greater than the effective distance between their respective points of pivotal connection to the frame and tread when the latter is in firm contact with the readbed, a second lever pivoted medially of its ends to a xed point on the frame, a link connecting `an end of said second lever to the forward end of the first lever, a crank mounted for rotation on the frame and having an eccentric crank arm, means operatively connecting the other end of the connecting link and crank arm in driving relationship whereby rotation of the crank will eifect oscillation of the second lever, a motor on said frame, and means operatively connecting the motor and crank in driving relationship.

References Cited in the tile of this patent UNITED STATES PATENTS 255,496 Depp Mar. 28, 1882 339,831 Abt Apr. 13, 1886 2,272,429 Philbrick Feb. l0, 1942 2,491,064 Urschel Dec. 13, 1949 2,714,357 Talboys Aug. 2, 1955 FOREIGN PATENTS 524,910 France May 24, 1921 308,707 Germany Oct. 2 6, 1918 

